The present invention is related to a sensor for sensing stress and more particularly to a sensor that utilizes magnetostrictive properties of material to sense stress caused by torque.
Magnetostrictive sensors for sensing stress are relatively well known. Further, magnetostrictive sensors for sensing torque via stress sensing are known. In general, magnetostrictive sensors utilize the magnetostrictive properties associated with ferromagnetic materials to sense stress, from torque or the like, applied to an object.
Ferromagnetic materials have magnetostrictive properties that have an interaction relationship with mechanical energy. For instance, when a mechanical energy, such as an external force, is applied to a ferromagnetic material, magnetic properties, such as magnetic permeability, of the material change.
U.S. Pat. No. 5,144,846 discloses a magnetostrictive stress and torque sensor. The patent discloses that stress and torque are sensed based on the principle of magnetostriction.
Similarly, U.S. Pat. No. 5,850,045 discloses a magnetostrictive stress sensor and U.S. Pat. No. 4,933,580 discloses a magnetostrictive torque sensor.
In accordance with one aspect, the present invention provides a sensor for sensing stress applied to an object. A first core member is aligned substantially parallel to the direction of applied stress. A second core member is aligned substantially perpendicular to the direction of applied stress. A central core portion connects the first and second core members. An excitation coil is operatively associated around the central core portion. The excitation coil produces a magnetic flux within the object and the first and second core members. A first detection coil is operatively associated around the first core member. A second detection coil is operatively associated around the second core member. The first and second detection coils detect changes in magnetic flux as affected by applied stress.
In accordance with another aspect, the present invention provides a sensor for sensing stress applied to an object. A grain-aligned portion has grains aligned in a direction parallel or perpendicular to the direction of stress. The grain-aligned portion is operatively associated with the object such that stress applied to the object is applied to the grain-aligned portion in a direction parallel or perpendicular to the direction of grain alignment. A core is located proximate to the grain-aligned portion. The core includes a center portion and first and second members. The first member extends from the center portion in a direction substantially parallel to the direction of grain alignment and terminates at a first end distal from the center portion. The second member extends from the center portion in a direction substantially perpendicular to the direction of grain alignment and terminates at a second end distal from the center portion. An excitation coil generates magnetic flux within the core and the grain-aligned portion. The coil is operatively associated around the core near the center portion of the core. A first detection coil develops a first metric in response to the generated magnetic flux. The first metric changes when the magnetic flux changes as a result of applied stress. The first detection coil is operatively associated around the first member near the first end of the first member. A second detection coil develops a second metric in response to the generated magnetic flux. The second metric changes when the magnetic flux changes as a result of applied stress. The second detection coil is operatively associated around the second member near the second end of the second member. The first and second detection coils are operatively connected such that the first and second metrics are summed together to increase the sensitivity of the sensor.
In accordance with another aspect, the present invention provides a sensor for sensing stress applied to an object. A grain-aligned portion has grains aligned in a direction parallel or perpendicular to the direction of stress. The grain-aligned portion is operatively associated with the object such that stress applied to the object is applied to the grain-aligned portion in a direction parallel or perpendicular to the direction of grain alignment. First detection means, aligned parallel to the direction of stress, detects changes in a characteristic of the portion that changes as a result of applied stress. The first detection means develops a first detection metric that changes in response to changes in the characteristic that occur in a direction parallel to the direction of applied stress. The first detection means outputs a first signal indicative of the changes in the metric. Second detection means, aligned perpendicular to the direction of stress, detects changes in the characteristic. The second detection means develops a second detection metric that changes in response to changes in the characteristic that occur in a direction perpendicular to the direction of applied stress. The second detection means outputs a second signal indicative of the changes in the metric. The first and second detection means are operatively connected such that the first and second output signals are summed together.
In accordance with another aspect, the present invention provides a sensor for sensing stress applied to an object. The sensor is operatively associated with the object such that stress applied to the object is also applied to the sensor. Detection means detects changes in a characteristic of the object that changes as a result of applied stress. The detection means develops a detection metric functionally related to the characteristic. The detection metric changes when the characteristic changes. The sensor outputs a signal indicative of more than twice the change in the developed metric.
In accordance with yet another aspect, the present invention provides a sensor for sensing stress applied to an object. A grain-aligned portion has grains aligned in a direction parallel or perpendicular to the direction of stress. The grain-aligned portion is operatively associated with the object such that stress applied to the object is applied to the grain-aligned portion in a direction parallel or perpendicular to the direction of grain alignment. Detection means detects changes in a characteristic of the portion. The characteristic changes as a result of applied stress. The detection means develops a detection metric functionally related to the characteristic. The detection metric changes in response to changes in the characteristic. The sensor outputs a signal indicative of more than two times the change in the developed metric.
In accordance with still another aspect, the present invention provides a sensor for sensing torque applied to a shaft. A magnetostrictive portion is associated with the shaft such that torque applied to the shaft stresses the magnetostrictive portion. A magnetic core is located proximate the magnetostrictive portion. The core has a central portion and a plurality of portions remote from the central portion. An electrically conductive excitation coil produces a magnetic flux in the core. The excitation coil is operatively associated around the core near the central portion of the core. A plurality of electrically conductive detection coils, across which a voltage is developed in response to the produced magnetic flux as affected by torque, are operatively associated around the remote portions of the core.
In accordance with yet still aspect, the present invention provides a sensor for sensing torque applied to a shaft. A magnetostrictive portion is associated with the shaft such that torque applied to the shaft stresses the magnetostrictive portion. A magnetic core is located proximate the magnetostrictive portion. The core has an origin and an arm extending there-from. An electrically conductive excitation coil produces a magnetic flux in the core. The excitation coil is operatively associated around the core near the origin of the core. An electrically conductive detection coil, across which a voltage is developed in response to the produced magnetic flux as affected by torque, is operatively associated around the arm of the core.